I'm adding a shower in the basement (there was a half-bathroom already) and the new drain is literally right by the stack (probably few feet away, 3-4' max), so I would think the air coming from the stack itself (which is vented in the upper floors) would be more than enough to prevent any siphoning here, but I want to make sure that is the case and find out what code says about it. What are the conditions for a pipe to be acceptable as a wet-vent?

And, if I can't use that as a wet-vent, would an inline vent (like sure-vent) suffice in my case?

Thank you in advance for your insights.

a simple schematic of the setup



here is an actual image ( the Pex pipes are only there to get the copper pipes out of way! )

I also draw where the new shower drain will go and the possibility of a cheater vent in the wall.

A picture of the set-up!

  • 2
    A photo of the two items in question may shed more light. What is the diameter of the vent pipe you speak of? And the size of the shower drain? As long as you know that is a vent stack or drain tied to a vent, it should prevent the shower trap from getting suction assuming any other item in that bathroom is down-line from the point the shower trap runs to a main drain. But if a toilet is upstream from the shower trap, it could suck the shower trap before there is a chance for the drain to have vent.
    – CCCBuilder
    Sep 12, 2019 at 0:22
  • Thank you @Nic for the helpful insight, I didn't think about the fact that hpstair toilet flash may suck the water out of the p-trap in the basement. I added a photo to the original post. There were, however, already a toilet in the basement, with no additional vent, as you can see in the photo.
    – mim
    Sep 16, 2019 at 3:28

2 Answers 2


Generally speaking: A Stack (even if it's vented) is not a Vent if it has a toilet on it above the point you want to use it as a vent. Older installs may not respect this. There were problems with not respecting this, code changed to solve them.

You can run a (dry) vent up to a point "6 inches (or more) above the flood rim of the highest fixture on the floor served" and join to the Stack where it IS a vent. In that case it would be the highest floor served, but you can join vents for the basement 6 inches above the flood rim of the highest fixture in the basement - but you can't then join that to a stack with a toilet above. You can run it parallel to the stack until you are 6" above the highest fixture and then join the stack.


An in-line vent will not work as it will provide an undesired venting of sewer gas into your basement. (Not to mention empty your shower trap as Nic described).

Is there a reason you do not want to install a dedicated vent? Exactly how are you connecting the new shower drain to the existing drain? Is this connection being made below grade? Are you ripping out concrete to make the connection?

  • I thought the in-line vents ( like Sure-vent or Studor ) only let air in and not out, hence no undesired effect ( I double checked in their specifications ) The reason I don't want to install a dedicated vent is because it adds a lot of work! the new shower is in the basement and there is no easy access to put a vent outside. The connection is below grade and I have had to rip out the concrete as you can see in the new photo I shared.
    – mim
    Sep 16, 2019 at 3:33
  • 1
    Theoretically that is how they operate--but I don't trust them long-term. The spring may weaken over time and/or the seal will develop leaks. (This has been my experience). Maybe it is not a bad solution if you have easy access to replace it every year or two(?).
    – peinal
    Sep 17, 2019 at 11:41
  • Yeah I am putting it in an access panel that Oatey makes for it ( it has holes to let the air in ), so it's pretty accessible, I'll probably just unscrew the old one and put a new one every other year
    – mim
    Sep 18, 2019 at 1:23
  • They fail, they stink, I'm willing to go to a fair bit of work to put in a real vent that does not fail and does not stink.
    – Ecnerwal
    Feb 10, 2021 at 2:03
  • It's been more than a year and I can say that not only it hasn't failed but also never smelled the slightest bit so far, to be honest, I don't see it failing even in the long run as it doesn't have any moving parts.. maybe except if it is installed in a very dusty area where dust can get under the membrane and keep it open? not sure.. And it really just lets the air in,
    – mim
    Feb 11, 2021 at 5:16

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